The instant invention is directed to a papermaking fabric for use in the press section of a papermaking machine.
Normally the papermaking fabrics formed for use in the press section comprise multi-layer fabrics formed with a woven or coil formed base fabric having a support fiber batt needled onto its upper surface. This basic structure presents certain problems due to the inherent density of the fiber batt and the large quantities of fluid which is extracted from the paper forming fibers. In use, the pressure exerted by the rolls of the press section for extracting the fluid also acts to compress the fiber batt. Compression of the fiber batt lowers the porosity of the papermaking fabric and reduces its effectiveness. U.S. Pat. Nos. 4,283,454; 4,842,925; and 5,618,612 show known fabrics of this general construction.
Another type press fabric now in use consists essentially of a woven fabric formed of monofilament yarns. These fabrics may be multi-layer with the upper layer being woven to provide a support surface which is more dense than the density of the support fabric. The effort here is to provide a support surface which presents uniform coverage so as to provide uniform drainage and also uniform markings on the paper product. Because of the stiffness and configuration of the monofilament forming yarns, there is a tendency for them to slip or change positions causing the support surface to become uneven which produces non-uniform drainage and non-uniform marks on the paper product. U.S. Pat. Nos. 4,161,195 and 4,518,644 illustrate the manner in which the monofilament yarns shift positions causing unevenness over the fabric surface.
The instant invention is intended to overcome these drawbacks by providing a papermaking fabric having a support which provides substantially uniform cover while at the same time is not subject to blockage as a result of extensive compression.
Accordingly, it is an object of the instant invention to provide a papermaking fabric of stable construction.
Another object of the invention is to provide a multi-layer papermaking fabric in which fabric layers are separate fabrics.
Another object of the invention is to provide in a papermaking fabric a support surface having expanded cover and adequate drainage.
Another object of the invention involves the utilization of knit yarns in the formation of the fabric forming the support surface, thereby providing increased cover.
Another object of the invention is to provide a papermaking fabric having increased and uniform cover along with improved fabric stability.